1. Field of the Invention
The invention relates to labeling, detecting, and/or isolating proteins with post-translational modifications.
2. Description of the Related Art
Protein glycosylation is one of the most abundant post-translational modifications and plays a fundamental role in the control of biological systems. For example, carbohydrate modifications are important for host-pathogen interactions, inflammation, development, and malignancy (1). One such covalent modification is O-GlcNAc glycosylation, which is the covalent modification of serine and threonine residues by β-N-acetylglucosamine (2). The O-GlcNAc modification is found in all higher eukaryotic organisms from C. elegans to man and has been shown to be ubiquitous, inducible and highly dynamic, suggesting a regulatory role analogous to phosphorylation. However, the regulatory nature of the modification (i.e., dynamic, low cellular abundance) also represents a central challenge in its detection and study.
A common method to observe O-GlcNAc involves labeling proteins with β-1,4-galactosyltransferase (GalT), an enzyme that catalyzes the transfer of [3H]-Gal from UDP-[3H]galactose to terminal GlcNAc groups (3). Unfortunately, this approach is expensive, involves handling of radioactive material, and requires exposure times of days to months. Antibodies (4,5) and lectins (3) offer alternative means of detection, but they can suffer from weak binding affinity and limited specificity.